Technical Field
The present invention relates to optical burst switching, and more particularly, to lossless and low-delay optical burst switching using soft reservations and opportunistic transmission.
Description of the Related Art
The rapid growth of internet traffic triggered by the emergence of new application, services, networking, paradigms and means of user connectivity is imposing ever-increasing demands on the network core. Despite the high-capacity offered by existing optical network backbones adopting wavelength division multiplexing WDM), it is evident that novel advances are required in order to keep up with the simultaneous increase in volume, diversity and dynamicity of traffic demands. Current optical core networks largely follow the traditional circuit switching approach for handling optical network resources. Under this paradigm optical circuits are formed, whereby resources (i.e. wavelengths) are reserved until explicitly torn down. The advantage of this approach is guaranteed performance, but this is achieved only under the premise of gross overprovisioning. Moreover, bursty traffic patterns cannot be handled by existing systems and methods, since resources are reserved for a connection even if there is no data actually transmitted—while other connections throughout the network might be in need of additional resources. The end result is poor network utilization and an inadequacy to support emerging services.
Several years ago, the Optical Burst Switching (OBS) concept was proposed for WDM optical networks in order to address the aforementioned issues. The main premise of OBS is the separation of control from data: A dedicated control channel (λ0) is reserved network-wide for carrying the so-call Burst Header Packets (BHPs). At the edge of the network, data traffic (e.g. coming from an IP router) is aggregated at an Optical Edge Node (OEN). Once a burst (e.g., consisting of a large number of packers) is assembled, the OEN creates a BHP carrying all necessary information to reserve the resources for the upcoming burst across all intermediate Optical Switching Nodes (OSN). The latter are basically optical cross-connects (OXCs) which also comprise a controller handling BHPs and performing burst scheduling based on the information extracted from them, with the help of a local scheduling log indicating already reserved resources for upcoming bursts.
In other words, the BHPs follow the same path that the actual burst will do and try to reserve resources in advance at each core node for a limited, duration, sufficient to receive and forward the burst. OBS manages to eliminate the need for buffering at intermediate core nodes (i.e. OSN), since reservations are made in advance for each burst. The latter is transmitted following a predetermined offset time after the BHP departure (enough to account for the BHP Optical-Electrical-Optical (O-E-O) conversions and electrical processing) and can then travel all-optically across the optical network. However, currently, OBS presently includes the very significant drawback of extreme burst loss even at a low network load.